There are a great many needs for sensor systems that can discriminate objects. Such discrimination can be, for example, plant discrimination for horticultural purposes, foreign object detection in industrial processes and in classification systems, to name just a few.
One particular area of interest is in the discrimination of pests in crops. Pests may include insects or weeds. In the area of weed control it is common practice to spray herbicides at different times in the cultivation cycle of a crop. Environmental concerns and increased farm costs have led -to critical evaluation of the use of chemicals in agriculture. Some farming practices have emerged which enable site specific application of chemicals such as herbicide, hence limiting the use of agro-chemicals. The ability to accurately identify and/or differentiate plants in real time and at common operating speeds of farm equipment is regarded as an unmet desire in agriculture.
One vegetation discriminating system known as “the Patchen Weed Seeker” discriminates by measuring the vegetation index (VI) defined as the ratio of reflection at near infrared wavelengths (at around 800 nm) to reflection at red wavelengths (around 650 nm). The VI is high for green plants and low for soil. However this system still has numerous problems including focusing of light from its LED light sources when the target object varies in distance from the LEDs and its ability to discriminate between different green plants with any reliability.